Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos construtores tinham uma grade de 13?
 ###Tabelas: CREATE TABLE chronological_list_of_grand_slam_singles_titles_leaders (chronological_list_of_grand_slam_singles_titles_leaders_id AUTO_INCREMENT PRIMARY KEY, Years led VARCHAR, Span of years led INT, Player VARCHAR, Titles won at point of lead INT, Total Career titles INT, Tournament at which lead began VARCHAR) CREATE TABLE historical_gdp_per_capita_nominal (historical_gdp_per_capita_nominal_id AUTO_INCREMENT PRIMARY KEY, Year VARCHAR, 2010 INT, 2009 INT, 2008 INT, 2005 INT, 2000 INT, 1995 INT, 1990 INT, 1985 INT) CREATE TABLE official_delegates (official_delegates_id AUTO_INCREMENT PRIMARY KEY, Country VARCHAR, Contestant VARCHAR, Age INT, Height (cm) INT, Height (ft) VARCHAR, Hometown VARCHAR) CREATE TABLE race_2;_1000cc_superbike_race_final_standings (race_2;_1000cc_superbike_race_final_standings_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Rider VARCHAR, Team VARCHAR, Time VARCHAR, Speed VARCHAR) CREATE TABLE race_results (race_results_id AUTO_INCREMENT PRIMARY KEY, Pos INT, Grid INT, Car INT, Driver VARCHAR, Constructor VARCHAR, Manufacturer VARCHAR, Laps INT, Laps Led INT, Points INT)  
SELECT COUNT Constructor FROM race_results WHERE Grid = 13